Fibroids can cause your cycles to be messed up, as well as adnormal bleeding and cramping. Your situation was what I was going through (bleeding one week on, one week off, one week on) and the OBGYN did an u/s, found small cysts on my ovaries and 2 fibroids on my uterus. He also believed I wasn't ovulating, which is why I was bleeding more than normal. He put me on Prometrium (progesterone supplment), I started bmy period AND ovulated on time.